1. Field of the Invention
The present invention broadly relates to a gas turbine engine and, more particularly, is concerned with a device to clear or eliminate a stall stagnation and to improve starting thereafter in a turbofan engine.
2. Description of the Prior Art
Various means have been used to detect and prevent stall in the compressors of gas turbine engines. Patents to Moore, U.S. Pat. No. 2,781,634; Herbst, U.S. Pat. No. 3,514,212; Boothe, U.S. Pat. No. 3,671,134; and Speigner et al U.S. Pat. No. 3,868,625, illustrate various transducer systems for detecting the onset of surge or stall in the fan or compressor portion of the engine in time for corrective action to be taken to prevent complete engine flow breakdown or stagnation.
Fan or compressor surge or stall occurs when the fan or compressor attempts to operate at a pressure (or pressure ratio) against which it cannot provide positive (in the normal direction) flow. At this condition the onset of surge or stall occurs.
Fan engines have two principle problem areas. First, they are susceptible to fan surge or stall due to the happening of augmentor anomalies, such as blowout followed by relight or mislights, and resultant core engine stagnation. Second, they experience small relight windows (relative to a normal turbojet engine) due to the low airflow resistance through the fan duct relative to the core engine. Consequently, inlet airflow passes around the core engine rather than through it where the airflow is needed to obtain relight core speed.
However, for the fan or compressor of a turbofan engine to stall there are three conditions which must be present. First, there must be a member of the system that can store energy and return it (like a spring). In the F100 engine, this is the gaseous volume downstream of the fan or compressor. Second, the airflow must be free to travel in either direction, i.e., no check valves. Third, there must be some kind of disturbance in the system to initiate the problem, such as augmentor blowout or augmentor mislight, followed by ignition and resultant pressure spike. If any one of these conditions is absent, surge will not occur.
A need exists for a solution to the aforementioned problems which does not require a transducer to sense the onset of surge or stall and then, in turn, cause actuation of something else to prevent or correct the problem. The time delay between sensing of surge and actuation of corrective measures may be unacceptable.